The present invention relates to a system for measuring pressure in a brain ventricle of a hydrocephalic patient or the like, and more particularly to a brain ventricle shunt which is implanted in the body of the patient by operation.
Generally, it is necessary to accurately measure pressure in the brain ventricle in order to diagnose cranial nerve trouble.
Heretofore, various measuring means have been proposed. For example, "Remote pressure sensor for a brain ventricle shunt system" is disclosed in "Surg. Neurol" Vol. 11, April, 1979.
As shown in FIGS. 17 and 18, the remote pressure sensor for the brain ventricle shunt system comprises a brain ventricle shunt 50 and a pressure detecting device 60.
The brain ventricle shunt 50 is constructed of a fine tubular brain ventricle catheter 51 to be inserted into the brain ventricle, a shunt main body 52 connected to the brain ventricle 51 and including a reservoir and a pump chamber, and a tubular peritoneum or auricle catheter 53 connected to the shunt main body and to be inserted into the peritoneum or the auricle.
As shown in FIG. 18, the shunt main body 52 is implanted on a skull 17 under a scalp 16. Inside the shunt main body, there is provided a relief valve 54 composed of a miter valve or the like, which is closed and opened by means of the pressure of the cerebrospinal fluid, which is an excrement fluid from the brain ventricle. A flexible diaphragm 55 is formed on an upper portion of the main body 52 to be upwardly expanded by the pressure of the cerebrospinal fluid passing through the chamber under the diaphragm. A stopper 56 is provided on a lower portion of the chamber, corresponding to the diaphragm 55.
A pressure sensor 57 of the pressure detecting device 60 is embedded in the main body 52 at a lower portion thereof. The sensor 57 comprises a tuning circuit 58 having a resonator such as a coil embedded in the main body 52, and a tuning element 59 provided on a wall forming diaphragm 55 for changing the resonance frequency in accordance with the distance from the tuning circuit 58.
The pressure detecting device 60 has other elements disposed outside the body of the patient. That is, there are provided an antenna 61 for transmitting electromagnetic waves to the pressure sensor 57 for detecting the resonance frequency thereof, and an indicator 62 for indicating the resonance frequency of a signal supplied to the antenna 61. A non-metallic pressure applying member 63 is disposed between the scalp 16 and the antenna 61. The member 63 is supplied with compressed air from a compressed air supply device 64. When the member 63 is expanded by the compressed air, the tuning element 59 is moved closer to the tuning circuit 58. Further, a pressure guage 65 for detecting the pressure of the compressed air is provided in the device 60.
Describing the measuring operation.
(1) The antenna 61 is disposed at a detecting position. The diaphragm 55 is pressed by a finger through the scalp 16 to cause the tuning element 59 to approach the tuning circuit 58. The indicator 62 receives a signal from the antenna 61 and the calibration of the indicator is performed.
(2) When the finger is removed, it is confirmed that the diaphragm 55 is outwardly expanded to separate the tuning element 59 from the tuning circuit 58, and that the indication of indicator 62 is away from the calibration range.
(3) The pressure applying member 63 is inserted between the scalp 16 and the antenna 61 and expanded to press the diaphragm 55. At the time the indicator 62 indicates the calibration range, the pressure on the pressure guage 65 corresponds to the pressure in the brain ventricle.
However, the tuning circuit 58 and the tuning element 59 in the head have influence on electromagnetic waves radiated from a scanner such as the CT scanner and neuclear magnetic resonance scanner. Accordingly, these elements interfere with the forming of a tomogram by such a scanner. Further, the structure of the system is complicated, and it is difficult to perform the calibration with accuracy.